The present invention relates to a filled silicone composition and more particularly to a filled silicone composition containing a hydrophobic partially aggregated colloidal silica. The present invention also relates to a cured silicone product formed from the composition.
Silicones are useful in a variety of applications by virtue of their unique combination of properties, including high thermal stability, good moisture resistance, excellent flexibility, high ionic purity, low alpha particle emissions, and good adhesion to various substrates. In particular, silicones containing a reinforcing filler, such as treated silica, are commonly employed in applications requiring exceptional mechanical properties. For example, filled silicones are widely used in the automotive, electronic, construction, appliance, and aerospace industries.
Silicone compositions containing hydrophobic non-aggregated colloidal silica are known in the art. For example, Kwan et al. disclose a silicone composition containing a vinyl-terminated polydimethylsiloxane, and Sixe2x80x94H functional crosslinker, a hydrophobic colloidal silica, and a platinum catalyst. (156th ACS Rubber Division Meeting, Orlando, Fla., September 1999, paper 96).
U.S. Pat. No. 6,051,672 to Burns et al. discloses a silicone rubber composition comprising hydrophobic non-aggregated colloidal silica prepared by a method comprising reacting an aqueous suspension of a hydrophilic non-aggregated colloidal silica having an average particle diameter greater than about 4 nm with a silicon compound selected from the group consisting of organosilanes and organosiloxanes at a pH less than about pH 4 in the presence of a sufficient quantity of a water-miscible organic solvent to facilitate contact of the hydrophilic non-aggregated colloidal silica with the silicon compound at a temperature within a range of about 20 C to 25 C for a time period sufficient to form a hydrophobic non-aggregated colloidal silica.
Although, the aforementioned silicone compositions cure to form silicone products having a wide range of mechanical properties, high concentrations, for example, 60% w/w, of hydrophobic non-aggregated colloidal silica are typically required to achieve superior mechanical properties. Consequently, there is a need for a filled silicone composition containing a low concentration of a hydrophobic colloidal silica that cures to form a silicone product having excellent mechanical properties.
The present invention is directed to a filled silicone composition comprising:
(A) a curable silicone composition; and
(B) 5 to 60% (w/w) of a hydrophobic partially aggregated colloidal silica.
The present invention is also directed to a cured silicone product comprising a reaction product of the above-described filled silicone composition.
The filled silicone composition of the present invention has numerous advantages including low VOC (volatile organic compound) content and good flow. Moreover, the filled silicone composition cures to form a cured silicone product having excellent mechanical properties, such as durometer hardness, tensile strength, elongation, modulus, and tear strength, at relatively low concentrations compared with a similar silicone composition lacking the hydrophobic partially aggregated colloidal silica. The potential advantages of low filler concentrations include shorter formulation time, lower cost, and lower viscosity.
The filled silicone composition of the present invention has numerous uses including adhesives, sealants, encapsulants, and molded articles, such as o-rings.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
A filled silicone composition according to the present invention comprises:
(A) a curable silicone composition; and
(B) 5 to 60% (w/w) of a hydrophobic partially aggregated colloidal silica.
Component (A) is a curable silicone composition. Curable silicone compositions and methods for their preparation are well known in the art. Examples of curable silicone compositions include, but are not limited to, hydrosilylation-curable silicone compositions, peroxide curable silicone compositions, condensation-curable silicone compositions, epoxy-curable silicone compositions; ultraviolet radiation-curable silicone compositions, and high-energy radiation-curable silicone compositions. For example, a suitable hydrosilylation-curable silicone composition typically comprises (i) an organopolysiloxane containing an average of at least two silicon-bonded alkenyl groups per molecule, (ii) an organohydrogensiloxane containing an average of at least two silicon-bonded hydrogen atoms per molecule in an amount sufficient to cure the composition, and (iii) a hydrosilylation catalyst. The hydrosilylation catalyst can be any of the well known hydrosilylation catalysts comprising a platinum group metal, a compound containing a platinum group metal, or a microencapsulated platinum group metal-containing catalyst. Platinum group metals include platinum, rhodium, ruthenium, palladium, osmium and iridium. Preferably, the platinum group metal is platinum, based on its high activity in hydrosilylation reactions.
The hydrosilylation-curable silicone composition can be a one-part composition or a multi-part composition comprising the components in two or more parts. Room-temperature vulcanizable (RTV) compositions typically comprise two parts, one part containing the organopolysiloxane and catalyst and another part containing the organohydrogensiloxane and any optional ingredients. Hydrosilylation-curable silicone compositions that cure at elevated temperatures can be formulated as one-part or multi-part compositions. For example, liquid silicone rubber (LSR) compositions are typically formulated as two-part systems. One-part compositions typically contain a platinum catalyst inhibitor to ensure adequate shelf life.
A suitable peroxide-curable silicone composition typically comprises (i) an organopolysiloxane and (ii) an organic peroxide. Examples of organic peroxides include, diaroyl peroxides such as dibenzoyl peroxide, di-p-chlorobenzoyl peroxide, and bis-2,4-dichlorobenzoyl peroxide; dialkyl peroxides such as di-t-butyl peroxide and 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane; diaralkyl peroxides such as dicumyl peroxide; alkyl aralkyl peroxides such as t-butyl cumyl peroxide and 1,4-bis(t-butylperoxyisopropyl)benzene; and alkyl aroyl peroxides such as t-butyl perbenzoate, t-butyl peracetate, and t-butyl peroctoate.
A condensation-curable silicone composition typically comprises (i) an organopolysiloxane containing an average of at least two hydroxy groups per molecule; and (ii) a tri- or tetra-functional silane containing hydrolysable Sixe2x80x94O or Sixe2x80x94N bonds. Examples of silanes include alkoxysilanes such as CH3Si(OCH3)3, CH3Si(OCH2CH3)3, CH3Si(OCH2CH2CH3)3, CH3Si[O(CH2)3CH3]3, CH3CH2Si(OCH2CH3)3, C6H5Si(OCH3)3, C6H5CH2Si(OCH3)3, C6H5Si(OCH2CH3)3, CH2xe2x95x90CHSi(OCH3)3, CH2xe2x95x90CHCH2Si(OCH3)3, CF3CH2CH2Si(OCH3)3, CH3Si(OCH2CH2OCH3)3, CF3CH2CH2Si(OCH2CH2OCH3)3, CH2xe2x95x90CHSi(OCH2CH2OCH3)3, CH2xe2x95x90CHCH2Si(OCH2CH2OCH3)3, C6H5Si(OCH2CH2OCH3)3, Si(OCH3)4, Si(OC2H5)4, and Si(OC3H7)4; organoacetoxysilanes such as CH3Si(OCOCH3)3, CH3CH2Si(OCOCH3)3, and CH2xe2x95x90CHSi(OCOCH3)3; organoiminooxysilanes such as CH3 Si[Oxe2x80x94Nxe2x95x90C(CH3)CH2CH3]3, Si[Oxe2x80x94Nxe2x95x90C(CH3)CH2CH3]4, and CH2xe2x95x90CHSi[Oxe2x80x94Nxe2x95x90C(CH3)CH2CH3]3; organoacetamidosilanes such as CH3Si[NHC(xe2x95x90O)CH3]3 and C6H5Si[NHC(xe2x95x90O)CH3]3; aminosilanes such as CH3Si[NH(s-C4H9)]3 and CH3Si(NHC6H11)3; and organoaminooxysilanes.
A condensation-curable silicone composition can also contain a condensation catalyst to initiate and accelerate the condensation reaction. Examples of condensation catalysts include, but are not limited to, amines; and complexes of lead, tin, zinc, and iron with carboxylic acids. Tin(II) octoates, laurates, and oleates, as well as the salts of dibutyl tin, are particularly useful. The condensation-curable silicone composition can be a one-part composition or a multi-part composition comprising the components in two or more parts. For example, room-temperature vulcanizable (RTV) compositions can be formulated as one-part or two-part compositions. In the two-part composition, one of the parts typically includes a small amount of water.
A suitable epoxy-curable silicone composition typically comprises (i) an organopolysiloxane containing an average of at least two epoxy-functional groups per molecule and (ii) a curing agent. Examples of epoxy-functional groups include 2-glycidoxycthyl, 3-glycidoxypropyl, 4-glycidoxybutyl, 2,(3,4-epoxycyclohexyl)ethyl, 3-(3,4-epoxycyclohexyl)propyl, 2,3-epoxypropyl, 3,4-epoxybutyl, and 4,5-epoxypentyl. Examples of curing agents include anhydrides such as phthalic anhydride, hexahydrophthalic anhydride, tetrahydrophthalic anhydride, and dodecenylsuccinic anhydride; polyamines such as diethylenetriamine, triethylenetetramine, diethylenepropylamine, N-(2-hydroxyethyl)diethylenetriamine, N,Nxe2x80x2-di(2-hydroxyethyl)diethylenetriamine, m-phenylenediamine, methylenedianiline, aminoethyl piperazine, 4,4-diaminodiphenyl sulfone, benzyldimethylamine, dicyandiamide, and 2-methylimidazole, and triethylamine; Lewis acids such as boron trifluoride monoethylamine; polycarboxylic acids; polymercaptans; polyamides; and amidoamines.
A suitable ultraviolet radiation-curable silicone composition typically comprises (i) an organopolysiloxane containing radiation-sensitive functional groups and (ii) a photoinitiator. Examples of radiation-sensitive functional groups include acryloyl, methacryloyl, mercapto, epoxy, and alkenyl ether groups. The type of photoinitiator depends on the nature of the radiation-sensitive groups in the organopolysiloxane. Examples of photoinitiators include diaryliodonium salts, sulfonium salts, acetophenone, benzophenone, and benzoin and its derivatives.
A suitable high-energy radiation-curable silicone composition comprises an organopolysiloxane polymer. Examples of organpolyosiloxane polymers include polydimethylsiloxanes, poly(methylvinylsiloxanes), and organohydrogenpolysiloxanes. Examples of high-energy radiation include xcex3-rays and electron beams.
Component (B) is at least one hydrophobic partially aggregated colloidal silica. As used herein, the term xe2x80x9chydrophobic partially aggregated colloidal silicaxe2x80x9d refers to the product prepared by a method comprising reacting (1) a silica sol comprising at least one hydrophilic partially aggregated colloidal silica with (2) an organosilicon compound selected from (a) at least one organosilane having the formula R1aHbSiX4-a-b, (b) at least one organocyclosiloxane having the formula (R12SiO)m, (c) at least one organosiloxane having the formula R13SiO(R1SiO)nSiR13, and (d) a mixture comprising at least two of (a) (b), and (c), in the presence of (3) water (4) an effective amount of a water-miscible organic solvent, and (5) an acid catalyst, to produce the hydrophobic partially aggregated colloidal silica and an aqueous phase, wherein R1 is hydrocarbyl or substituted hydrocarbyl; X is a hydrolysable group; a is 0, 1, 2, or 3; b is 0 or 1; a+b=1, 2, or 3, provided when b=1, a+b=2 or 3; m has an average value of from 3 to 10; and n has an average value of from 0 to 10.
Component (1) is a silica sol comprising at least one hydrophilic partially aggregated colloidal silica. As used herein, the term xe2x80x9csilica solxe2x80x9d refers to a stable suspension of hydrophilic partially aggregated colloidal silica particles in water, an organic solvent, or a mixture of water and a water-miscible organic solvent. Also, as used herein, the term xe2x80x9chydrophilicxe2x80x9d means the silica surface has silanol (Sixe2x80x94OH) groups capable of hydrogen bonding with suitable donors, such as adjacent silanol groups and water molecules. In other words, the silanol groups produced during manufacture of the silica have not been modified, for example, by reaction with an organic or organosilicon compound. Further, as used herein, the term xe2x80x9cpartially aggregated colloidal silicaxe2x80x9d refers to colloidal silica comprising particles having a ratio D1/D2 of at least 3, where D1 is the mean diameter of the colloidal silica particles measured by a dynamic light-scattering method and D2 is the mean diameter of the colloidal silica particles as determined by a nitrogen adsorption method, and D1 has a value of from 40 to 500 nm. The value of D1 can be determined using a conventional light-scattering apparatus according to the well known method described in J. Chem. Phys. 1972, 57 (11), 4814. The value of D2 can be calculated according to the equation D2=2720/S, where S is the specific surface area of the colloidal silica as determined by nitrogen absorption according to the Brunauer-Emmett-Teller (BET) method. Additionally, aqueous silica sols typically have a pH of from 7 to 11.
Examples of silica sols suitable for use as component (1) include, but are not limited to, a moniliform silica sol disclosed by Watanabe et al. in European Patent Application No. EP 1114794 A1 and an elongated-shaped silica sol disclosed by Watanabe et al. in U.S. Pat. No. 5,597,512. The moniliform (rosary- or pearl necklace-shaped) silica sol has an SiO2 concentration of 1 to 50% (w/w) and contains liquid medium-dispersed moniliform colloidal silica particles having a ratio D1/D2 of at least 3, wherein the moniliform colloidal silica particles comprise spherical colloidal silica particles having a mean diameter of 10 to 80 nm and metal oxide-containing silica bonding the spherical colloidal silica particles, wherein the spherical colloidal silica particles are linked in rows in only one plane; and D1 and D2 are as defined above, wherein D1 has a value of from 50 to 500 nm. The length of the moniliform colloidal silica particles is typically at least five times the mean diameter of the spherical colloidal silica particles, as determined by electron micrographs. The silica bonding the spherical colloidal silica particles contains a small amount, 0.5 to 10% (w/w), of a divalent or trivalent metal oxide, based on the weight of SiO2 in the silica bonding the spherical colloidal silica particles, depending on the method of preparing the moniliform silica sol.
The moniliform silica sol typically contains not greater than 50% (w/w), preferably 5 to 40% (w/w), of SiO2. The viscosity of the silica sol is typically from several mPaxc2x7s to about 1,000 mPaxc2x7s at room temperature.
Examples of moniliform silica sol include the aqueous suspensions of colloidal silica sold by Nissan Chemical Industries, Ltd. (Tokyo, Japan) under the trade names SNOWTEX-PS-S and SNOWTEX-PS-M, described in the Examples section below.
The moniliform silica sol can be prepared as described in detail by Watanabe et al. in European Patent Application No. EP 1114794 A1. Briefly stated, the method comprises: (a) adding an aqueous solution containing a water-soluble divalent metal salt or a water-soluble trivalent metal salt singly or in admixture to an active silicic acid-containing aqueous colloidal liquid or an acidic silica sol having a mean particle diameter of 3 to 8 nm, each containing 0.5 to 10% (w/w) of SiO2 and having a pH of 2 to 6, in an amount of 1 to 10% (w/w) as a metal oxide based on SiO2 in the aqueous colloidal solution of active silicic acid or acidic silica sol and mixing them; (b) adding acidic spherical silica sol having a mean diameter of 10 to 80 nm and a pH 2 to 6 to the mixed liquid (a) obtained in step (a) in such an amount that a ratio of a silica content (A) derived from the acidic spherical silica sol to a silica content (B) derived from the mixed liquid (b), A/B (weight ratio), is 5 to 100 and the total silica content (A+B) of a mixed liquid (b) obtained by mixing the acidic spherical silica sol with the mixed liquid (a) has an SiO2 concentration of 5 to 40% (w/w) in the mixed liquid (b) and mixing them; (c) adding an alkali metal hydroxide, water-soluble organic base or water-soluble silicate to the mixed liquid (b) obtained in step (b) such that the pH is 7 to 11 and mixing them; and (d) heating the mixed liquid (c) obtained in step (c) at 100 to 200xc2x0 C. for 0.5 to 50 h.
The elongated-shaped silica sol has an SiO2 concentration of 6 to 30% (w/w) and contains elongated-shaped amorphous colloidal silica particles having a ratio D1/D2 of at least 5, wherein D1 and D2 are as defined above for the moniliform colloidal silica particles and D1 has a value of from 40 to 300 nm; and the particles are elongated in only one plane and have a uniform thickness along the elongation within the range of from 5 to 20 nm, as determined using an electron microscope. The colloidal silica particles are substantially amorphous silica, but they may contain a small amount, typically 1500 to 8500 ppm, of an oxide of calcium or magnesium, or both, based on the weight of SiO2 in the silica sol. In some cases, the silica particles may contain a slight amount of oxides of other polyvalent metals in addition to the oxides of calcium and/or magnesium. The total concentration of metal oxides is typically from 1500 to 15000 ppm, based on the weight of SiO2 in the silica sol. Examples of polyvalent metals include strontium, barium, zinc, tin, lead, copper, iron, nickel cobalt, manganese, aluminum, chromium, yttrium, and titanium.
The elongated-shaped silica sol can be prepared as described in detail by Watanabe et al. in U.S. Pat. No. 5,597,512. Briefly stated, the method comprises: (a) mixing an aqueous solution containing a water-soluble calcium salt or magnesium salt or a mixture of said calcium salt and said magnesium salt with an aqueous colloidal liquid of an active silicic acid containing from 1 to 6% (w/w) of SiO2 and having a pH in the range of from 2 to 5 in an amount of 1500 to 8500 ppm as a weight ratio of CaO or MgO or a mixture of CaO and MgO to SiO2 of the active silicic acid; (b) mixing an alkali metal hydroxide or a water-soluble organic base or a water-soluble silicate of said alkali metal hydroxide or said water-soluble organic base with the aqueous solution obtained in step (a) in a molar ratio of SiO2/M2O of from 20 to 200, where SiO2 represents the total silica content derived from the active silicic acid and the silica content of the silicate and M represents an alkali metal atom or organic base molecule; and (c) heating at least a part of the mixture obtained in step (b) to 60xc2x0 C. or higher to obtain a heel solution, and preparing a feed solution by using another part of the mixture obtained in step (b) or a mixture prepared separately in accordance with step (b), and adding said feed solution to said heel solution while vaporizing water from the mixture during the adding step until the concentration of SiO2 is from 6 to 30% (w/w). The silica sol produced in step (c) typically has a pH of from 8.5 to 11.
Component (1) can be a silica sol comprising a single hydrophilic partially aggregated colloidal silica as described above or a silica sol comprising two or more such colloidal silicas that differ in at least one property, such as surface area, pore diameter, pore volume, particle size, and particle shape.
Component (2) is at least one organosilicon compound selected from (2)(a), (2)(b), (2)(c), and (2)(d), each described below.
Component (2)(a) is at least one organosilane having the formula R1aHbSiX4-a-b, wherein R1 is hydrocarbyl or substituted hydrocarbyl; X is a hydrolysable group; a is 0, 1, 2, or 3; b is 0 or 1; and a+b=1, 2, or 3, provided when b=1, a+b=2 or 3. The groups and substituted hydrocarbyl groups represented by R1 typically have from 1 to 20 carbon atoms, alternatively from 1 to 10 carbon atoms, alternatively from 1 to 6 carbon atoms. Acyclic hydrocarbyl and substituted hydrocarbyl groups containing at least 3 carbon atoms can have a branched or unbranched structure.
Examples of hydrocarbyl groups include, but are not limited to, alkyl, such as methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, pentyl, 1-methylbutyl, 1-ethylpropyl, 2-methylbutyl, 3-methylbutyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, and octadecyl; cycloalkyl, such as cyclopentyl, cyclohexyl, and methylcyclohexyl; aryl, such as phenyl and naphthyl; alkaryl, such as tolyl and xylyl; aralkyl, such as benzyl and phenethyl; alkenyl, such as vinyl, allyl, and propenyl; arylalkenyl, such as styryl and cinnamyl; and alkynyl, such as ethynyl and propynyl.
Examples of substitutents include xe2x80x94OH, xe2x80x94NH2, xe2x80x94SH, xe2x80x94CO2H, xe2x80x94O(Oxe2x95x90C)CR2, xe2x80x94(R2)N(Oxe2x95x90)CR2, and xe2x80x94Sxe2x80x94Sxe2x80x94R2, wherein R2 is C1 to C8 hydrocarbyl.
As used herein, the term xe2x80x9chydrolysable groupxe2x80x9d The term xe2x80x9chydrolysable groupxe2x80x9d means the Si-X group can react with water to form an Sixe2x80x94OH group. Examples of hydrolysable groups include, but are not limited to, xe2x80x94Cl, Br, xe2x80x94OR3, xe2x80x94OCH2CH2OR3, CH3C(xe2x95x90O)Oxe2x80x94, Et(Me)Cxe2x95x90Nxe2x80x94Oxe2x80x94, CH3C(xe2x95x90O)N(CH3)xe2x80x94, and xe2x80x94ONH2, wherein R3 is C1 to C8 hydrocarbyl or halogen-substituted hydrocarbyl.
Examples of hydrocarbyl groups represented by R3 include, but are not limited to, unbranched and branched alkyl, such as methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl, 1,1-dimethylethyl, pentyl, 1-methylbutyl, 1-ethylpropyl, 2-methylbutyl, 3-methylbutyl, 1,2-dimethylpropyl, 2,2-dimethylpropyl, hexyl, heptyl, and octyl; cycloalkyl, such as cyclopentyl, cyclohexyl, and methylcyclohexyl; phenyl; alkaryl, such as tolyl and xylyl; aralkyl, such as benzyl and phenethyl; alkenyl, such as vinyl, allyl, and propenyl; arylalkenyl, such as styryl; and alkynyl, such as ethynyl and propynyl. Examples of halogen-substituted hydrocarbyl groups include, but are not limited to, 3,3,3-trifluoropropyl, 3-chloropropyl, chlorophenyl, and dichlorophenyl.
Examples of organosilanes include, but are not limited to, SiCl4, CH3SiCl3, CH3CH2SiCl3, C6H5SiCl3, (CH3)2SiCl2, (CH3CH2)2SiCl2, (C6H5)2SiCl2, (CH3)3SiCl, CH3HSiCl2, (CH3)2HSiCl, SiBr4, CH3SiBr3, CH3CH2SiBr3, C6H5SiBr3, (CH3)2SiBr2, (CH3CH2)2SiBr2, (C6H5)2SiBr2, (CH3)3SiBr, CH3HSiBr2, (CH3)2HSiBr, Si(OCH3)4, CH3Si(OCH3)3, CH3Si(OCH2CH3)3, CH3Si(OCH2CH2CH3)3, CH3Si[O(CH2)3CH3]3, CH3CH2Si(OCH2CH3)3, C6H5Si(OCH3)3, C6H5CH2Si(OCH3)3, C6H5Si(OCH2CH3)3 CH2xe2x95x90CHSi(OCH3)3, CH2xe2x95x90CHCH2Si(OCH3)3, CF3CH2CH2Si(OCH3)3, (CH3)2Si(OCH3)2, (CH3)2Si(OCH2CH3)2, (CH3)2Si(OCH2CH2CH3)2, (CH3)2Si[O(CH2)3CH3]2, (CH3CH2)2Si(OCH2CH3)2, (C6H5)2Si(OCH3)2, (C6H5CH2)2Si(OCH3)2, (C6H5)2Si(OCH2CH3)2, (CH2xe2x95x90CH)2Si(OCH3)2, (CH2xe2x95x90CHCH2)2Si(OCH3)2, (CF3CH2CH2)2Si(OCH3)2, (CH3)3SiOCH3, CH3HSi(OCH3)2, (CH3)2HSiOCH3, CH3Si(OCH2CH2OCH3)3, CF3CH2CH2Si(OCH2CH2OCH3)3, CH2xe2x95x90CHSi(OCH2CH2OCH3)3, CH2xe2x95x90CHCH2Si(OCH2CH2OCH3)3, and C6H5Si(OCH2CH2OCH3)3, (CH3)2Si(OCH2CH2OCH3)2, (CF3CH2CH2)2Si(OCH2CH2OCH3)2, (CH2xe2x95x90CH)2Si(OCH2CH2OCH3)2, (CH2xe2x95x90CHCH2)2Si(OCH2CH2OCH3)2, (C6H5)2Si(OCH2CH2OCH3)2, CH3Si(OAc)3, CH3CH2Si(OAc)3, CH2xe2x95x90CHSi(OAc)3, (CH3)2Si(OAc)2, (CH3CH2)2Si(OAc)2, (CH2xe2x95x90CH)2Si(OAc)2, CH3Si[ONxe2x95x90C(CH3)CH2CH3]3, (CH3)2Si[ONxe2x95x90C(CH3)CH2CH3]2, CH3Si[NHC(xe2x95x90O)CH3]3, C6H5Si[NHC(xe2x95x90O)CH3]3, (CH3)2Si[NHC(xe2x95x90O)CH3]2, and Ph2Si[NHC(xe2x95x90O)CH3]2, wherein OAc is CH3C(xe2x95x90O)Oxe2x80x94 and Ph is phenyl.
Component (2)(a) can be a single organosilane or a mixture comprising two or more different organosilanes, each having the formula R1aHbSiX4-a-b, wherein R1, X, a, and b are as defined above. Methods of preparing organosilanes suitable for use as component (2)(a) are well known in the art; many of these organosilanes are commercially available.
Component (2)(b) is at least one organocyclosiloxane having the formula (R12SiO)m, wherein R1 is as defined and exemplified above for component (2)(a) and m has an average value of from 3 to 10, alternatively from 3 to 8, alternatively from 3 to 5.
Examples of organocylclosiloxanes include, but are not limited to, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, and decamethylcyclopentasiloxane.
Component (2)(b) can be a single organocylcosiloxane or a mixture comprising two or more different organocyclosiloxanes that differ in at least one property, such as structure, viscosity, average molecular weight, siloxane units, and sequence. Methods of preparing organocyclosiloxanes suitable for use as component (2)(b) are well known in the art; many of these organocyclosiloxanes are commercially available.
Component (2)(c) is at least one organosiloxane having the formula R13SiO(R1SiO)nSiR13, wherein R1 is as defined and exemplified above for component (2)(a) and n has an average value of from 0 to 10, alternatively from 0 to 8, alternatively from 0 to 4.
Examples of organosiloxanes include, but are not limited to, hexamethyldisiloxane, hexaethyldisiloxane, 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, octamethyltrisiloxane, and decamethyltetrasiloxane.
Component (2)(c) can be a single organosiloxane or a mixture comprising two or more different organosiloxanes that differ in at least one property, such as structure, viscosity, average molecular weight, siloxane units, and sequence. Methods of preparing organosiloxanes suitable for use as component (2)(c) are well known in the art; many of these organosiloxanes are commercially available.
Component (2) can be a single organosilicon compound represented by components (2)(a), (2)(b), and (2)(c), or a mixture comprising at least two of the components.
Component (4) is at least one water-miscible organic solvent. As used herein, the term xe2x80x9cwater-misciblexe2x80x9d means the organic solvent is substantially miscible with water or completely miscible (i.e., miscible in all proportions) with water. For example, the solubility of the water-miscible organic solvent in water is typically at least 90 g/100 g of water at 25xc2x0 C.
Examples of water-miscible organic solvents include, but are not limited to, monohydric alcohols such as methanol, ethanol, 1-propanol, and 2-propanol; dihydric alcohols such as ethylene glycol and propylene glycol; polyhydric alcohols such as glycerol and pentaerythritiol; and dipolar aproptic solvents such as N,N-dimethylformamide, tetrahydrofuran, dimethylsulfoxide, and acetonitrile. Component (4) can be a single water-miscible organic solvent or a mixture comprising two or more different water-miscible organic solvents, each as defined above.
Component (5) is at least one acid catalyst that promotes reaction of the hydrophilic partially aggregated colloidal silica with the organosilicon compound, component (2). Although the acid catalyst is typically added as a separate component to the reaction mixture, in some cases it can be produced in situ. For example, when component (2) is an organosilane containing a hydrolysable group such as chloro, a portion or all of the acid catalyst may be generated by reaction of the chlorosilane with water or the hydroxy groups of the hydrophilic partially aggregated colloidal silica.
Examples of acid catalysts include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, and hydrofluoric acid; and organic acids such as acetic acid, oxalic acid, and trifluoroacetic acid. The acid can be a single acid or a mixture comprising two or more different acids.
The method of the present invention can be carried out in any standard reactor suitable for contacting silica with an organosilicon compound in the presence of water and an acid catalyst. Suitable reactors include glass and Teflon-lined glass reactors. Preferably, the reactor is equipped with an efficient means of agitation, such as a stirrer.
The silica sol, component (1), is typically added to a mixture comprising the organosilicon compound, water, the water-miscible organic solvent, and the acid catalyst. Reverse addition, i.e., addition of a mixture comprising the organosilicon compound to the silica sol is also possible. However, reverse addition may result in formation of larger aggregates of the colloidal silica.
The rate of addition of the silica sol to the mixture containing the organosilicon compound is typically from 1 to 3 mL/min for a 0.5-L reaction vessel equipped with and efficient means of stirring. When the rate of addition is too slow, the reaction time is unnecessarily prolonged. When the rate of addition is too fast, the colloidal silica may form larger aggregates.
The suspension of the hydrophilic partially aggregated colloidal silica and the organosilicon compound are typically reacted at a temperature of from 20 to 150xc2x0 C., alternatively from 40 to 120xc2x0 C., alternatively from 60 to 100xc2x0 C. When the temperature is less than 40xc2x0 C., the rate of reaction is typically very slow.
The reaction is carried out for a period of time sufficient to produce the hydrophobic partially aggregated colloidal silica, and an aqueous phase. The reaction time depends on a number of factors including the nature of the hydrolysable groups in the organosilicon compound, structure of the organosilicon compound, agitation of the reaction mixture, concentration of the hydrophilic partially aggregated colloidal silica, and temperature. The reaction time is typically from several minutes to several hours. For example, the reaction time is typically from 0.1 to 2 h at a temperature of from 40 to 120xc2x0 C., alternatively from 0.5 to 1 h at a temperature of from 60 to 100xc2x0 C. The optimum reaction time can be determined by routine experimentation using the methods set forth in the Examples below.
The concentration of the hydrophilic partially aggregated colloidal silica of component (1) in the reaction mixture is typically from 1 to 20% (w/w), alternatively from 1 to 10% (w/w), alternatively from 1 to 5% (w/w), based on the total weight of the reaction mixture.
The mole ratio of the organosilicon compound, component (2), to the hydrophilic partially aggregated colloidal silica (SiO2) of component (1) is typically from 0.1 to 5, alternatively from 0.2 to 3, alternatively from 0.5 to 2. When the mole ratio of component (2) to the hydrophilic partially aggregated colloidal silica is less than 0.1, the treated silica may not exhibit hydrophobic properties. When the mole ratio is greater than 5, the hydrophobic colloidal silica may not precipitate from the aqueous phase, as described below.
The concentration of water, component (3), in the reaction mixture is typically from 20 to 60% (w/w), alternatively from 20 to 50% (w/w), alternatively from 20 to 40% (w/w), based on the total weight of the reaction mixture. When component (1) is an aqueous silica sol, a portion or all of component (3) may be supplied by the silica sol.
The water-miscible organic solvent, component (4), is present in an effective amount in the reaction mixture. As used herein, the term xe2x80x9ceffective amountxe2x80x9d means the concentration of component (4) is such that the organosilicon compound is soluble in the aqueous reaction mixture containing the water-miscible organic solvent, and the partially aggregated colloidal silica particles in the reaction mixture are stable, i.e., the particles do not form larger aggregates. Aggregation of the hydrophilic partially aggregated colloidal silica particles can be detected by comparing the size and shape of the hydrophobic colloidal silica particles with the size and shape of the hydrophilic partially aggregated colloidal silica particles of component (1) using electron microscopy. The concentration of component (4) is typically from about 5 to about 35% (v/v), alternatively from 10 to 30% (v/v), alternatively from 20 to 30% (v/v), based on the total volume of the reaction mixture. When the concentration of component (4) is less than 5% (v/v), the treated silica may not exhibit hydrophobic properties. When the concentration of component (4) is greater than 35% (v/v), the hydrophobic colloidal silica may not precipitate from the aqueous phase, as described below. The effective amount of component (4) can be determined by routine experimentation using the methods in the Examples below.
The concentration of component (5) is sufficient to maintain the pH of the reaction mixture at a value less than 4. For example, the concentration of component (5) is typically from 10 to 60% (w/w), alternatively from 10 to 40% (w/w), based on the total weight of the reaction mixture. When the concentration of component (5) is less than 10% (w/w), the rate of reaction may be too slow for commercial applications. When the concentration of component (5) is greater than 60% (w/w), additional washing steps may be required to remove the acid from the hydrophobic partially aggregated colloidal silica.
The hydrophobic partially aggregated colloidal silica typically precipitates from the aqueous phase. As used herein, the term xe2x80x9cprecipitatesxe2x80x9d means the hydrophobic partially aggregated colloidal silica forms a deposit that is insoluble in the aqueous phase. For example, the hydrophobic colloidal silica may float to the top of the aqueous phase, settle to the bottom of the aqueous phase, or collect on the walls of the reaction vessel. The hydrophobic silica is typically separated from the aqueous phase by removing (for example, draining or decanting) the aqueous phase or the hydrophobic silica.
The hydrophobic silica, isolated as described above, is typically washed with water to remove residual acid. The water can further comprise a water-miscible organic solvent, such as 2-propanol. The concentration of the water-miscible organic solvent in the aqueous wash is typically from 10 to 30% (v/v). The hydrophobic silica can be washed by mixing it with water and then separating the hydrophobic silica from the water. The organic phase is typically washed from one to three times with separate portions of water. The volume of water per wash is typically from two to five times the volume of the hydrophobic partially aggregated colloidal silica.
The washed hydrophobic silica is typically dried by suspending it in a water-immiscible organic solvent and then removing the organic solvent using a process such as evaporating or spray drying. As used herein, the term xe2x80x9cwater-immisciblexe2x80x9d means the organic solvent is slightly miscible or completely immiscible with water. For example, the solubility of water in the solvent is typically less than about 0.1 g/100 g of solvent at 25xc2x0 C. The organic solvent can be any aprotic or dipolar aprotic organic solvent that is immiscible with water. Preferably, the organic solvent forms a minimum boiling azeotrope with water. If the organic solvent does not form an azeotrope with water, the organic solvent preferably has a boiling point greater than the boiling point of water.
Examples of water-immiscible organic solvents include, but are not limited to, saturated aliphatic hydrocarbons such as n-pentane, hexane, n-heptane, isooctane and dodecane; cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as benzene, toluene, xylene and mesitylene; cyclic ethers such as tetrahydrofuran (THF) and dioxane; ketones such as methyl isobutyl ketone (MIBK); halogenated alkanes such as trichloroethane; and halogenated aromatic hydrocarbons such as bromobenzene and chlorobenzene. The water-immiscible organic solvent can be a single organic solvent or a mixture comprising two or more different organic solvents, each as defined above.
Additionally, before removing the water-immiscible organic solvent, as described above, the suspension of the hydrophobic silica in the organic solvent can be distilled to remove water. The distillation can be carried out at atmospheric or subatmospheric pressure at a temperature that depends on the boiling point of the water-immiscible organic solvent. The distillation is typically continued until the distillate is free of water.
Under certain conditions, the hydrophobic partially aggregated colloidal silica remains suspended in the aqueous phase of the reaction mixture. In this case, the aqueous suspension of the hydrophobic silica is typically treated with a water-immiscible organic solvent in an amount sufficient to form a non-aqueous phase comprising the water-immiscible organic solvent and the hydrophobic silica. Suitable water-immiscible organic solvents are described above. The concentration of the water-immiscible organic solvent is typically from 5 to 20% (v/v), alternatively from 10 to 20% (v/v), based on the total volume of the aqueous suspension.
The non-aqueous phase is typically separated from the aqueous phase by discontinuing agitation of the mixture, allowing the mixture to separate into two layers, and removing the aqueous or non-aqueous layer.
The non-aqueous phase, isolated as described above, is typically washed with water to remove residual acid. The water can further comprise a water-miscible organic solvent, such as 2-propanol. The concentration of the water-miscible organic solvent in the solution is typically from 10 to 30% (v/v). The non-aqueous phase can be washed by mixing it with water, allowing the mixture to separate into two layers, and removing the aqueous layer. The organic phase is typically washed from one to three times with separate portions of water. The volume of water per wash is typically from two to five times the volume of the non-aqueous phase.
The hydrophobic silica is typically dried by removing the water-immiscible organic solvent using a method such as evaporating or spray-drying.
Additionally, before removing the water-immiscible organic solvent, the non-aqueous phase can be distilled to remove water. The distillation can be carried out at atmospheric or subatmospheric pressure at a temperature that depends on the boiling point of the water-immiscible organic solvent. The distillation is typically continued until the distillate is free of water. The distillation is typically continued until the distillate is free of water.
The hydrophobic partially aggregated colloidal silica prepared by the method of the present invention typically has a surface area of from 20 to 300 m2/g, alternatively from 50 to 200 m2/g, alternatively from 50 to 150 m2/g, as determined by nitrogen adsorption according to the BET method. Also, the hydrophobic colloidal silica typically has a pore diameter of from 50 to 300 xc3x85, alternatively from 100 to 250 xc3x85, alternatively from 150 to 250 xc3x85; and a pore volume of from 0.5 to 1.5 mL/g, alternatively form 0.5 to 1.0 mL/g, as determined by nitrogen adsorption methods. Moreover, the hydrophobic colloidal silica comprises particles having a size and shape approximating the size and shape of the hydrophilic colloidal silica particles of component (a).
The hydrophobic partially aggregated colloidal silica of component (1) can be a single hydrophobic partially aggregated colloidal silica or a mixture comprising two or more such silicas differing in at least one property, such as surface area, pore diameter, pore volume, and hyrophobicity, particle size, and particle shape.
The concentration of component (B) in the filled silicone composition is typically from 5 to 60% (w/w), alternatively from 10 to 50% (w/w), alternatively from 20 to 40% (w/w), based on the total weight of the silicone composition. When the concentration of component (B) is less than 5% (w/w), the cured silicone product typically does not exhibit improved mechanical properties relative to the unfilled composition. When the concentration of component (B) is greater than 60% (w/w), the composition may be too viscous for certain applications. The effective amount of component (B) can be determined by routine experimentation using the methods in the Examples below.
The filled silicone composition of the present invention can comprise additional ingredients, provided the ingredient does not prevent the composition from curing to form a silicone product having superior mechanical properties. Examples of additional ingredients include, but are not limited to, hydrosilylation catalyst inhibitors, dyes, pigments, adhesion promoters, anti-oxidants, heat stabilizers, UV stabilizers, flame retardants, surfactants, flow control additives, and inorganic fillers.
The filled silicone composition of the instant invention is typically prepared by mixing components (A) and (B) and any optional ingredients in the stated proportions at ambient temperature with or without the aid of an organic solvent. Mixing can be accomplished by any of the techniques known in the art such as milling, blending, and stirring, in either a batch or continuous process. Alternatively, component (B) can be combined with the individual components of the curable silicone composition of component (A) in any order.
A cured silicone product according to the present invention comprises a reaction product of the filled silicone composition comprising components (A) and (B), described above. The filled silicone composition can be cured by exposure to ambient temperature, elevated temperature, moisture, or radiation, depending on the particular cure mechanism. For example, one-part hydrosilylation-curable silicone compositions are typically cured at an elevated temperature. Two-part hydrosilylation-curable silicone compositions are typically cured at room temperature or an elevated temperature. One-part condensation-curable silicone compositions are typically cured by exposure to atmospheric moisture at room temperature, although cure can be accelerated by application of heat and/or exposure to high humidity. Two-part condensation-curable silicone compositions are typically cured at room temperature; however, cure can be accelerated by application of heat. Peroxide-curable silicone compositions are typically cured at an elevated temperature. Epoxy-curable silicone compositions are typically cured at room temperature or an elevated temperature. Depending on the particular formulation, radiation-curable silicone compositions are typically cured by exposure to radiation, for example, ultraviolet light, gamma rays, or electron beams.
The filled silicone composition of the present invention has numerous advantages including low VOC (volatile organic compound) content and good flow. Moreover, the filled silicone composition cures to form a cured silicone product having excellent mechanical properties, such as durometer hardness, tensile strength, elongation, modulus, and tear strength, at relatively low concentrations compared with a similar silicone composition lacking the hydrophobic partially aggregated colloidal silica. The potential advantages of low filler concentrations include shorter formulation time, lower cost, and lower viscosity.
The filled silicone composition of the present invention has numerous uses including adhesives, sealants, encapsulants, and molded articles, such as o-rings.